In automatic milking systems the take off of teat cups has been automated for some time. Early systems for initiating take off were solely based on a timer. When the timer ran out, the teat cups were removed. The time had to be set as an average milking time for the whole herd of milking animals. This naturally meant that a substantial part of the heard were over-milked, i.e. the teat cups were not removed in due time, resulting in pain and injury for these animals, while another significant part were under-milked, resulting in lost milk production and thus lost profit.
To avoid the problems mentioned above, the take off is initiated, in more recent milking machines, based on the milk flow, the amount of drawn milk, or a combination thereof, and also possibly in combination with a timer. For milking machines employing a milk claw and where all four teat cups are taken off simultaneously, the take off is initiated based on the combined milk flow from all four teats. Since it is common that the milk flow from an individual teat ends relatively abruptly (FIG. 1), and each quarter for a specific animal contains different amount of milk, the milk flow stops at different times for each teat. This means that some quarters for an animal will be over-milked, when all milk is drawn from the quarter finishing last.
Since the milk flow and/or milk quantity is measured by a flow or quantity meter downstream of the teat and not measured at the teat cup, there will be a time delay between the actual ending of the milk flow and the measurement of decreased milk flow, resulting in some over-milking even for the last quarter.
In the case with individual quarter milking, as employed for instance in automatic robotic milking machines, the teat cups are removed individually and some of the problems mentioned above are reduced. However, the problem with the time delay between actual milk flow end and measured milk flow end still prevails.
In some milking systems, a scheme to reduce the effects of automatic milking during low milk flow, is employed, reducing the vacuum level in the teat receiving space during the initial stage of milking, when the animal has not yet been stimulated enough to let down the milk, and during the late stage when the milk flow is diminishing. By measuring the milk flow, the regulation of the vacuum level in the teat receiving space can be controlled. Even though the system improves the situation, by both caring for the animal as well as allow for drawing as much milk as possible, the regulation will not be optimal, since the measurement of the milk flow is delayed from the actual milk flow changes due to the milk flow meter being positioned away from the teat.
U.S. Pat. No. 6,009,832 “A method for controlling the milking of an animal and a milking machine” by the present inventor et al. disclose a method to control the milking intensity by monitoring the abrupt movement of a teat cup liner between an open and a closed position. This movement is an indication of the milk flow. The method require the consideration of certain milking machine related conditions, such as e.g. the length of different pipes, the effect of the vacuum pump etc. “Machine milking and Lactation” edited by A. J. Bramelyr F. H. Dodd, G. A. Mein & J. A. Bramley shortley discuss measuring vacuum levels in the mouthpiece of a teat cup liner.